The present invention relates to a method of fabrication of a semiconductor integrated circuit device; and, more particularly, the invention relates to technology for fabrication of semiconductor integrated circuit devices, including a step of polishing a thin film deposited on the surface of a semiconductor wafer by chemical-mechanical polishing (CMP).
One example of micro-fabrication technologies, which represent an important aspect in the packaging of integrated circuits on semiconductors at higher densities and in enhancing their performance, is the chemical-mechanical polishing method that is used for formation of grooves that provide isolation between elements, referred to as Shallow Groove Isolation (SGI), for planarization of interlayer dielectrics in a multilayer wiring formation step, and for formation of embedded metal wiring. This chemical-mechanical polishing technology is described, for example, in the U.S. Pat. No. 4,944,836.
The chemical-mechanical polishing method is characterized by the fact that the surface of a wafer is polished while a polishing slurry is supplied on a turntable on which a polishing pad made of hard resin is attached. A particulate abrasive, such as silica (silicon oxide), is used for the polishing slurry, which is formed by dispersing the abrasive in deionized water and adding an alkaline substance for pH control. However, a problem has been recognized in that micro scratches may occur on the wafer surface due to the presence of coagulated coarse particles in the slurry, when the wafer is being polished with a polishing slurry containing silica, causing a deterioration in the LSI manufacturing yield rate and reliability.
In Japanese Unexamined Patent Publication No. Hei 10(1998)-321588 (Kou et al.), a method is disclosed for preventing micro scratches from occurring on the wafer surface due to the presence of coagulated particles. According to the technique disclosed in this Publication, generally, in the chemical-mechanical step, deionized water is supplied on the polishing pad to maintain a continuously wet condition. In the polishing step, the polishing slurry is supplied on a polishing pad moistened with deionized water. However, the pH value of the polishing slurry containing silica is about 10–11, while the pH value of purified water is 7. For this reason, when the polishing slurry is supplied on a polishing pad moistened with deionized water, a large difference in the pH value between the polishing slurry and the deionized water causes coarse coagulated particles to be created in the polishing slurry, leading to micro scratches on the wafer surface.
To solve this problem, as described in the above-mentioned Publication, a method has been proposed in which the polishing pad is moistened with pH pre-adjusted deionized water so that its pH value is identical to that of the polishing slurry, and then the polishing slurry is supplied on the polishing pad. In addition, another method has been proposed in which a mixture of pH pre-adjusted deionized water and a polishing slurry mixed at a given ratio is prepared for application to the polishing pad. When an alkaline substance is used for the polishing slurry, an alkaline reagent should be used for the pH adjustment reagent; while, when an acid substance is used for the polishing slurry, an acid reagent should be used for the pH adjustment reagent. If the alkaline polishing slurry containing silica is used, KOH or NH4OH may be preferably used for the pH adjustment reagent.